Various types of reluctance rotary electric machines have been known. For example, a synchronous reluctance motor is configured to rotate its rotor in relation to its stator opposite thereto based on a rotating magnetic field produced by field windings mounted on the stator. A switched reluctance motor is configured to sequentially excite poles (stator poles) of its stator in a given direction of its rotor to thereby rotate the rotor. Such a synchronous reluctance motor has been widely well known, and such a switched reluctance motor is for example disclosed in Japanese Patent Application Publication No. 2002-136073.
The rotor of such a reluctance rotary electric machine is designed as a salient-pole soft magnetic rotor. Specifically, the rotor with a substantially cylindrical shape is provided with a plurality of pairs of salient poles circumferentially arranged in a circumferential direction of the rotor such that the salient poles of each pair have a circumferential pitch corresponding to an electric angle of π radians. The salient poles of each pair are magnetically short-circuited inside the rotor.
The salient poles of the salient-pole rotor can be configured such that an outer periphery of the rotor is formed with a plurality of pairs of salients each extending radially outward; these salients of each pair have a circumferential pitch of an electric angle of π radians. The salient poles of the salient-pole rotor can also be configured such that a plurality of flux barriers (slits) are arranged to be circumferentially spaced apart from each other. The latter of the salient pole structure is disclosed in Japanese Patent Application Publication No. 2002-165427.
Japanese Patent Application Publication No. 2006-246571 discloses a reluctance motor having a substantially annular cylindrical rotor. The rotor is formed at its outer periphery with a plurality of magnetic segments whose number is different from the number of stator poles arranged opposing the rotor in a rotational direction thereof. The reluctance motor with the magnetic segments is configured such that the stator poles sequentially pull the magnetic segments in the rotational direction to thereby create a reluctance torque.
Such various types of reluctance motors are however integrated with magnets, and therefore, the magnitude of the reluctance torque created by each of the reluctance rotary electric machines is lower than that of an Interior Permanent Magnet Synchronous Motor (IPMSM) whose rotor is integrated with a plurality of permanent magnets. This results that, in order to obtain a desired torque, a reluctance motor is greater in size than an IPMSM, causing an obstacle in vehicle installability and manufacturing cost.